Radio communications involves either one-way (e.g. selective call signalling or paging systems) or two-way communications (cellular, cordless telephone, or digital personal communication systems) over radio waves. Communication takes place on channels, comprising time division multiplexed (TDM) time slots or frequency division multiplexed (FDM) frequencies, or a combination thereof.
For various radio communications, fixed radio frequency spectrum are assigned. For example, in the United States, the Federal Communications Commission reserves various portions of the radio frequency spectrum to designated communication services. The radio frequency use is therefore limited to assigned services. The radio frequency use is more overtaxed within certain areas where the number of frequencies allocatable for communicating between radio transceivers in a system are severely limited.
As communication between radio transceivers is initiated, the system allocates a channel or channels for communication service therebetween. With the increase in radio communications, such as cellular and cordless telephone usage, the method for allocating channels must allocate channels utilizing the assigned frequencies in a manner to accommodate ever increasing concurrent users. Signal interference may result from multiple simultaneous usage of the same channel in neighboring geographical areas (co-channel interference) or usage of adjacent channels in the same geographical areas. The resulting interference reduces the level of system service quality. It is therefore a primary concern of the system operator to allocate channels for communication in a manner to allow the greatest efficiency of usage while reducing interference in order to maintain a certain level of service quality.
There are generally two types of channel allocation methods: fixed channel allocation and dynamic channel allocation. Fixed channel allocation methods fix the channel assignments during the entire course of operation. Since the channels are allocated only once, the fixed channel allocation method can be very time intensive and, therefore, have a good chance to provide a high level of channel reuse for any given conditions. Fixed channel allocation methods are simple and may approach being optimal in terms of channel reuse to any given traffic pattern for a given system. But the fixed channel allocation is not adaptive to a changing service environment. Also, to add or remove a base station from the system is cumbersome and fixed channel allocation methods are unable to automatically initialize the channel allocation.
Dynamic channel allocation methods, on the other hand, allocate channels in accordance with a method which is adaptive to traffic and environment changes. Since dynamic channel allocation methods do not assign channels, channels can be used in any area as needed. In addition, most dynamic channel allocation methods can initialize automatically. Unfortunately most of the existing dynamic channel allocation methods are too dynamic to have good performance in terms of channel reuse.
Secondarily, a portable handset for communication with the communication system must also determine the quality of the available channel for communicating with the base stations of the communication system. However, since the base stations may be in close proximity and using the same channels to communicate with different handsets, the determination of channel quality by simply measuring the power of a received carrier at the handset, including averaging the received signal signal power to reduce fading effects, may produce undesirable results. The carrier signal energy produced by two adjacent base stations may apparently show a good channel quality, while in reality, the interference between the two base stations may result in a low quality of reception at the handset.
Also, since the handset must be prepared to receive a call at any time, the handset must maintain its own list of available quality channels. This requires periodically scanning and determining the quality levels of the channels by the handset in order to maintain a handset channel list. However, since the handset is portable and battery powered, periodic scanning of all of the channels in order to maintain the handset channel list reduces the life of the battery of the handset.
It is preferable to maintain an optimally high quality channel interface between the handset and a base station while a call is in progress. However, if handsets were excessively engaging in a handover process between changing channel quality base stations of the communication system, the communication system would be overly burdened with base station handover information. The handover information is communicated within the system without charge to the user. Thus the expense is absorbed by the system owner and thus the system owner has reduced profitability. Furthermore, since the handover information may use the same communications links as user call conversations, the addition of the handover information to these communication links reduces the call throughput of the communication system.
Thus what is needed is a way to improve the channel quality measurement made by the handset. Also what is needed is a method of improving the battery life of the handset while scanning What is also needed is a method for regulating the amount of handovers occurring within the system. What is further needed is a method which allows for establishing a high quality channel between the base station and the handset, wherein both the handset and the base station make individual determinations on the quality of the channel and the resulting selected channel is a combination of the individual determinations.